We have one of those huge family tents and we solved our "wetness" by erecting our Big Top. Buy at least 100ft of marine rope, a 20'x30'tarp, and several bungees. Before you set up camp, put up the Big Top--double string the rope across the site at the halfway point, as high in the trees as you can. Standing on the picnic table will do it

Tie it off with as many sailor knots as you know. Throw the tarp over the rope and even it up. Drive the kids out of the middle where they're playing "fort". Tie two corners on one end to the trees with ropes and bungees, then tie the other two corners. Make sure one end is higher than the other for drainage. NOW put down the ground cloth, put up the tent and string your tacky lights.
Not only with a Big Top this size "float" over your tent, thereby eliminating that nasty "snapping" sound all night, it will provide shade in the intense summer sun AND keep you and all your stuff dry. When we put up the Big Top, people come from all over the campground to sit in our dry chairs and play cards in the rain.

Our whole outfit cost us about $30(the tarp we got at Big Lots for <$10)
Cathy--
hears circus music in the distance